If there is no struggle there is no progress. Those who profess to favor freedom and yet deprecate agitation are men who want crops without plowing up the ground; they want rain without thunder and lightning. They want the ocean without the awful roar of its many waters.

Lincoln, Abraham. "Speech at Cincinnati, Ohio, September 17, 1859." Abraham Lincoln: Speeches and Writings 1859-1865, edited by Don E. Fehrenbacher. Library of America, 1989.

Madison, James. "No. 51: How to maintain: make the parts check each other. Also, a federal system divides power further.--Madison (or Hamilton)." The Federalist: A Commentary on the Constitution of the United States, edited by Robert Scigliano. The Modern Library, 2001.

Lincoln, Abraham. "Second Inaugral Address, March 4, 1865." Abraham Lincoln: Speeches and Writings 1859-1865, edited by Don E. Fehrenbacher. Library of America, 2018.

Laozi [Lao Tzu]. "The Natural Way of Lao Tzu." A Source Book in Chinese Philosophy, translated by Wing-Tsit Chan. Princeton University Press, 1969, ch. 64.